cell division

• Cells must replicate and divide to produce new cells and therefore enable organisms to grow and survive. 

  • Eukaryotic organisms divide by mitosis and meiosis.
  • Prokaryotic organisms divide by binary fission.
• Human body cells usually have 23 pairs of chromosomes, one received from their mother and one from their father. This means they have 46 chromosomes altogether. 

  Before cells divide they must replicate their DNA so the new cells have their own copies.
• Eukaryotic cells divide via mitosis which is a vital stage of the cell cycle, produces 2 daughter cells that are identical to the original cell with the same number of chromosomes. 
• when not dividing= long strings

  when dividing= DNA coils into chromosomes

  when copied= forms X shaped chromosomes
• Multicellular organisms need to carry out mitosis in order to grow, repair and develop
• Zygotes undergo several rounds of mitosis to increase the number of cells and develop into embryos. Embryos then go through many more rounds of mitosis and differentiation to create fully formed foetuses. 
• Zygotes undergo several rounds of mitosis to increase the number of cells and develop into embryos.

  Embryos then go through many more rounds of mitosis and differentiation to create fully formed foetuses. 
• Organisms that reproduce asexually divide by mitosis.
• THE CELL CYCLE: 3 main stages

  Growth and DNA Replication:

  • The cell increases its SUBCELLULAR STRUCTURES, such as MITOCHONDRIA and RIBOSOMES.
  • The nucleus of the cell REPLICATE their DNA, forming two identical X-SHAPED CHROMOSOMES.

  Mitosis

  • The MEMBRANE of the nucleus breaks down
  • The Chromosomes align in the CENTRE of the cell and are then pulled apart to opposite ends of the cell by structures known as CELL FIBRES.

  Cell Division

  • New membranes form around each set of chromosomes to form TWO NUCLEI
  • The cytoplasm and cell membrane SPLIT to form TWO IDENTICAL DAUGHTER CELLS
• cell cycle